Questions and answers on COVID-19: Vaccines

1. Which COVID-19 vaccines are available in the EU?

The following COVID-19 vaccines have been granted conditional marketing authorisation at centralised level by the European Medicines Agency (EMA) for use in the EU:

  • Comirnaty (by BioNTech/Pfizer)
  • Spikevax (by ModernaTX, Inc.)
  • Vaxzevria (by Oxford/AstraZeneca)
  • COVID-19 Vaccine Janssen (by Janssen-Cilag International N.V.)

A limited number of national authorities in the EU have also authorised the use of other vaccines against COVID-19 disease available on the market within their own countries.

Other vaccines against COVID-19 are in various stages of development, testing and authorisation.

2. How is the safety of the COVID-19 vaccine monitored?

COVID-19 vaccines are developed following the same legal requirements for quality, safety and efficacy as for all other vaccines. Like all vaccines, the effects of COVID-19 vaccines are tested in the laboratory first, including in animals, and then in human volunteers before being approved.

The European Medicines Agency (EMA) evaluates COVID-19 vaccines against the same high standards as for all other vaccines before they are released for use.

Once the vaccines are in use, national authorities and the EMA continually monitor for any side effects that may occur in people who have received the vaccines.

To learn more about how vaccine safety is monitored in the EU, visit the European Vaccination Information Portal: Monitoring vaccine safety and reporting side effects.

3. Are COVID-19 vaccines effective?

COVID-19 vaccines are developed and authorised for use following the same legal requirements and high standards for quality, safety and efficacy as for all other vaccines. Prior to marketing authorisation, vaccine efficacy is assessed in clinical trials, establishing how well the vaccine works in preventing COVID-19 disease of any severity.

Benefits of a vaccine may include

  • preventing the disease in the first place
  • reducing the number of people infected
  • reducing the number of severe cases of a disease as well as the number of deaths.

Regulators such as the European Medicines Agency (EMA) approve vaccines once studies confirm that the vaccine’s benefits exceed any potential risk.

Following conditional marketing authorisation and deployment of COVID-19 vaccines, observational studies collect data on how effective the vaccines are in real life, allowing for the monitoring of how they work in a timely manner.

Studies have been ongoing in the EU/EEA, including studies funded by the ECDC, and in other parts of the world since the vaccines started to be administered. Results are published regularly.

These studies look at how effective vaccines are in different situations such as

  • preventing infection
  • preventing transmission
  • preventing severe disease, hospitalisation, and death
  • acting against the different variants circulating, such as the Delta variant of concern
  • protecting specific population groups (e.g. older age groups).

Results from observational studies carried out to date show that the vaccines centrally authorised in the EU/EEA are currently highly protective against COVID-19-related severe disease, hospitalisation and death. Although overall high, effectiveness can however vary, depending on the population groups (e.g. among elderly populations) and the vaccine product.

For the vaccines that require two doses, effectiveness studies have also shown that it is important to take the second dose for the best protection, especially for the Delta variant.

The effectiveness of vaccines needs to be continuously monitored. This is key to detecting any signs of reduced protection or lower effectiveness against variants circulating. This is an area of evolving evidence, and vaccine recommendations may need to be adjusted accordingly.

4. How is ECDC supporting the vaccination rollout?

The development of strategies and national plans for the deployment of COVID-19 vaccines is the responsibility of EU/EEA countries. This also includes what population groups are prioritised for COVID-19 vaccination at the national level, and the vaccine rollout.

ECDC supports these efforts by working closely with EU/EEA countries and the European Commission to monitor the rollout of COVID-19 vaccines and to develop scientific evidence and relevant technical guidance, that can inform national priorities and decision-making.

ECDC also facilitates dialogue and exchanges between countries, supports preparedness activities, and provides a regular overview of vaccination deployment strategies and plans.

5. What are ECDC’s recommendations regarding COVID-19 vaccination?

ECDC strongly encourages those who are eligible for vaccination but have not yet been vaccinated to get fully vaccinated against COVID-19 in a timely manner according to national recommendations.

6. Do vaccinated individuals still need to follow personal protective measures?

Results from observational studies carried out to date show that the vaccines centrally authorised in the EU/EEA are currently highly protective against COVID-19-related severe disease, hospitalisation and death.

Until enough people are vaccinated, vaccinated individuals should continue to follow public health measures as per national recommendations. The pandemic is not over yet.

The highly transmissible Delta variant of SARS-CoV-2 is circulating in all EU/EEA countries, and in some areas and some population groups, not enough people are vaccinated. More evidence is needed to see how effective COVID-19 vaccines are at preventing transmission of this variant. Therefore, everyone, regardless of vaccination status, should follow the relevant national recommendations to mitigate the spread of the disease.

In settings with people at high risk of severe disease, such as long-term care facility residents, measures to limit transmission of SARS-CoV-2 virus are still needed. Even though vaccination coverage in long-term care facilities is usually very high, there is evidence of waning immunity following vaccination in some older people.

Therefore, measures are particularly important for residents who are more vulnerable, due to the aging of their immune system and the existence of other health conditions.

Measures can include, for example, the use of face masks for all long-term care facility workers regardless of their vaccination status, and for all contacts, particularly when indoors, as well as ensuring that physical distancing is possible during personal contacts with residents and between residents.

7. Will COVID-19 vaccines stop the pandemic?

Vaccines are a powerful tool in ensuring public health, and COVID-19 vaccines are playing an important role to control the pandemic. In the first phases of the vaccination campaigns, the main objective was to protect those who were most at risk from severe disease and reduce the burden on healthcare systems. More time is needed until more people are vaccinated and in specific areas and population groups, such as in younger age groups.

Studies are ongoing on how effective the current vaccines are in reducing SARS-CoV-2 transmission. In the meantime, all measures for controlling the spread of this virus – physical distancing, appropriate hand hygiene, respiratory etiquette, and the use of face masks, where required – remain of key importance.

8. Can COVID-19 vaccines protect people against the virus when it has mutated?

Vaccines against some viral diseases remain effective for many years and provide long-lasting protection. Others, such as the seasonal flu vaccines, need to be regularly updated to remain effective. This is because viruses constantly mutate when they circulate among people.

Many SARS-CoV-2 mutations have no impact on vaccine effectiveness, but some may be of concern due to a potential reduction in how well the existing vaccines may work. Scientists around the world are carefully monitoring mutations of SARS-CoV-2 virus to assess how well the currently available COVID-19 vaccines can protect people against them. Studies done to date show that the vaccines approved in the EU/EEA are currently highly protective against COVID-19-related severe disease, hospitalisation and death, also in the context of the circulation of the highly transmissible Delta variant. Vaccine producers are exploring ways to update vaccines as necessary to improve protection as new variants are detected.

9. Is COVID-19 vaccination still necessary, even after getting the disease and recovering?

Re-infection with COVID-19 occurs, although it is relatively rare. Also, at this point we do not know precisely how long people are naturally protected from getting COVID-19 again after clearing an infection. Follow-up periods for previously-infected individuals are not yet long enough to be able to draw conclusions on the duration of protection against infection beyond six months after infection. As a result, COVID-19 vaccination is recommended even for those who have recovered from the disease.

10. How long does immunity after COVID-19 vaccination last?

Early evidence suggests that immunity decreases over time and some people may again become infected with SARS-CoV-2. However data available to date tells us that  vaccine effectiveness continues to be strong against hospitalisation and severe disease. However, this needs to be carefully monitored over time, particularly among older adults where some signs of decreased protection against hospitalisations have now been reported by some countries.

The emergence and dominance of the Delta variant might have some impact on vaccine effectiveness and duration of protection after vaccination.. It is currently not known how long the immunity gained by COVID-19 vaccination will last. This will be further assessed by studies.

11. What percentage of the population should be vaccinated to achieve herd immunity?

The idea of herd immunity is that there is a certain proportion of people who need to be protected from a virus, either by vaccination or by having been infected, for the virus to stop spreading and die out.

For COVID-19, in practice, this would require a very high proportion of people in every community, every social group and every geographical location to have lasting protection against even mild disease.

This is very difficult to achieve due to the ease with which the newer variants of the virus spread, possible waning vaccine protection and the many reasons for which some people will not be vaccinated (including e.g. access issues, hesitancy, young children not being eligible for vaccination). However, vaccination remains an essential and powerful tool in reducing the number of people who will suffer from COVID-19.

12. How is COVID-19 vaccination progressing in the EU/EEA?

Vaccination campaigns against COVID-19 are underway in all EU/EEA countries. The ECDC Vaccine Tracker provides information on the national uptake of the first and second doses of COVID-19 vaccines by age and other target groups, as well as by vaccine products, for EU/EEA countries. It is complemented by the weekly COVID-19 vaccines rollout overview report, which provides key figures and additional data as of the previous week.

13. How effective is protection conferred after a single dose of COVID-19 vaccines requiring two doses?

Available data, across different population groups and SARS-CoV-2 variants confirm that protection against infection and severe disease given by two vaccine doses of Comirnaty, Spikevax or Vaxzevria is significantly higher than with partial vaccination (i.e. one dose of a two-dose regimen).

Preliminary evidence indicates that individuals who are partially vaccinated are less protected against symptomatic infection with the Delta variant than against the Alpha variant, regardless of the vaccine type. However, full vaccination provides good protection against severe disease caused by the Delta variant.

In the context of increasing circulation of the Delta variant, full vaccination should be achieved as early as possible and the second vaccine dose should be administered after the shortest possible interval recommended by the vaccine manufacturer. Priority should be given to population groups at highest risk of severe disease following SARS-CoV-2 infection.

14. For individuals previously infected with COVID-19 disease, is a single dose of a two-dose vaccine schedule sufficient?

Of the four COVID-19 vaccines currently authorised for use in the EU/EEA, three of them have two doses: Comirnaty, Spikevax and Vaxzevria.

For individuals that have recovered from a prior SARS-CoV-2 infection, studies indicate that a single dose of Comirnaty, Spikevax or Vaxzevria generates antibody and cellular immune responses that are comparable - in the short term - to individuals who did not have the disease previously and who received two doses.

However, assessing the immune response in people in these studies typically occurs between one and four weeks after the first dose, and there is not much data to compare the long-term duration of protective immunity for such individuals with people who did not have the disease and have completed a two-dose regimen. In addition, data concerning protection from the Delta variant are limited.

No evidence is currently available on the risk of infection and symptomatic disease for previously-infected individuals receiving just one dose of vaccine intended as a two-dose regimen.

As there are limited data for clinical outcomes as well as how long immune responses for a single dose last in previously infected individuals, ECDC continues to support the continued administration of a two-dose regimen as per EMA authorisation.

15. Are combined or so-called ‘mixed’ vaccination schedules using two different vaccines safe and effective?

Combined, heterologous or often referred to as ‘mixed’ COVID-19 vaccinations schedules involve using one vaccine for the first dose and a different vaccine for the second dose.

Mixed vaccine schedules are not new in the area of immunisation and thishas been done in the past for vaccines other than those against COVID-19 disease. In the case of COVID-19, a good immune response could be expected from combining different COVID-19 vaccines, as all licensed vaccines induce an immune response against the SARS-CoV-2 spike protein, and mixing vaccines could potentially boost the immune response.

Studies are currently ongoing in this area, and evidence from studies on mixed vaccination schedules suggests that the combination of Vaxzevria (as first dose) and mRNA vaccines (as a second dose) induces a better immune response against SARS-CoV-2 than using the same vaccine for both doses. Mixed vaccine schedules were generally well tolerated.

Several EU/EEA countries are currently using mixed vaccine schedules, mainly using a first dose of Vaxzevria followed with a second dose of an mRNA vaccine (Comirnaty or Spikevax). This is especially used to complete the vaccinations if there are severe reactions after the first dose or for other precautionary reasons based on national protocols. Current evidence provides scientific grounds to expect these ‘off-label’ approaches (prescription of a drug in a different way than it has been officially approved) to be safe and to create a satisfactory immune response.

16. Is an additional dose or a booster dose of a COVID-19 vaccine necessary?

Based on the current evidence on vaccine effectiveness and duration of protection, at this time there is no urgent need to give booster doses to fully vaccinated individuals in the general population.

However, close monitoring of vaccine effectiveness data, particularly among vulnerable groups at risk of severe COVID-19 and among those living in closed settings, should continue. If vaccines become less effective in one or more population groups, decisions should be adapted accordingly.

Additional doses should be considered for people with severely weakened immune systems. This dose would not be considered a ‘booster’, but an extension of the primary vaccination series as these persons may not be adequately protected from the primary series. An additional dose could also be considered as a preventative measure to older frail individuals, in particular those living in closed settings (e.g. long-term care facilities). This is due to emerging evidence that in older age groups and residents in long-term care facilities, vaccines can become less effective.

Booster doses are given to fully vaccinated people (i.e. people who have completed a primary vaccination) to restore protection after it has waned. More solid data are needed to inform future policies on booster doses. The European Medicines Agency (EMA) assesses the data on additional doses and on booster doses in order to consider whether updates to the product information are appropriate.

In the context of many countries outside of the EU/EEA still struggling to receive and administer enough doses of vaccine to their populations, special consideration should be given to the current global shortage of COVID-19 vaccines that could be further worsened by the administration of booster COVID-19 vaccine doses for the general population in the EU/EEA countries.

17. Should adolescents and/or younger population groups be vaccinated against COVID-19 disease?

The COVID-19 vaccine Comirnaty is approved in the EU for use in children aged 12 to 15 years (this vaccine had been already approved for people above 16 years and above). The COVID-19 vaccine Spikevax is approved for use in children aged 12 to 17. Since the approval, EU/EEA countries have initiated vaccination in younger age groups. Some are focusing on children with underlying health conditions, while other countries are including all children in these age groups in their vaccination programme.

The decision of whether to include younger population groups in the COVID-19 vaccination programme is taken at national level, after safety and effectiveness have been demonstrated in clinical trials and the vaccines authorised for these age groups. For this, countries usually consider a number of factors such as: national prioritisation strategies and how well the vaccine rollout has progressed in the priority groups, the risks and benefits of COVID-19 vaccination in different age groups of adolescents, the epidemiological situation and the population groups where disease continues to spread.

18. How worried should we be about ‘breakthrough’ infections (infections occurring in vaccinated people)?

Although COVID-19 vaccines authorised in the EU/EEA are highly effective, no vaccine is 100% effective. A minority of those who have been fully vaccinated may still get infected, particularly among the elderly and those with underlying health conditions. For example, variants that are more contagious have been implicated in outbreaks of breakthrough infections in long-term care facilities, where residents are more vulnerable due to the aging of the immune system and having other health conditions.

Evidence from studies on COVID-19 vaccine effectiveness conducted so far shows that, even if full vaccination is highly effective against symptomatic and severe infections, breakthrough infections that occur can sometimes lead to hospitalisations and deaths among vulnerable individuals. This can be serious if the virus is introduced in healthcare settings. People with other health conditions and/or low immunity are at highest risk of breakthrough infection and subsequent severe illness, so measures to further protect them should be considered.

Page last updated 12 Oct 2021