FAQs about COVID-19 vaccines

Over 13.7 billion doses of COVID-19 vaccines have been administered worldwide. This provides sufficient evidence to conclude that additional booster doses reduce the risk of severe disease, hospitalisation and death. Vaccines also reduce the risk of infection, although to a lesser extent.

In a study conducted by the WHO European Respiratory Surveillance Network, it was estimated that 1.6 million deaths were prevented in Europe thanks to the availability of COVID-19 vaccines between December 2020 and March 2023. Most of the deaths averted occurred among older adults, reinforcing the importance of up-to-date vaccination for those at higher risk.

The effectiveness of the original COVID-19 vaccines begins to decline around 3 months after administration, although protection against severe disease continues for an average of 6-9 months.

Many studies indicate the benefit of administering booster doses with mRNA vaccines every 6-12 months to maintain adequate protection against variants of the Omicron variants.

The continued emergence of new variants of concern (VOCs) may reduce the effectiveness of COVID-19 vaccines.

Current variants differ substantially from the ancestral Wuhan strain, requiring updates to vaccine formulations.

In adults aged ≥18 years with severe underlying conditions or immunosuppression, receiving an updated COVID-19 vaccine provides greater protection against disease-associated hospitalisation compared with not receiving an updated vaccine.

(data updated to August 2024). At least 70.7% of the global population received at least one dose of a COVID-19 vaccine, and 35.7% had received a booster dose.

The evidence obtained from the administration of billions of doses within such a short period represents a unique situation in the history of vaccination. Never before has the effectiveness and safety of a vaccine been studied so extensively. The data collected and analysed show that COVID-19 vaccines have a very favourable safety profile across all age groups and that their benefits outweigh potential risks.

Side effects following COVID-19 vaccination vary from person to person.

Most individuals experience no side effects or only mild, temporary reactions, such as pain at the injection site, fatigue, headache or muscle pain.

Booster doses of COVID-19 vaccines, particularly mRNA and protein-based vaccines, consistently demonstrate a favourable safety profile, with protein-based vaccines generally being associated with a lower risk of side effects.

A small number of potentially serious allergic reactions have been reported following COVID-19 vaccination, such as anaphylaxis, airway swelling or the development of a widespread skin rash, as can occur with any vaccine.

These reactions are very rare, typically occurring within minutes of vaccination and can be successfully treated.

In rare cases of individuals with a clear history of severe allergic reactions after an mRNA COVID-19 vaccine, the use of a protein-based vaccine may be considered as an alternative.

A few very uncommon safety concerns have been identified with the current vaccines. An international study analysed more than 99 million vaccinated individuals to investigate potential links with known rare adverse events.

In rare cases, the use of mRNA vaccines has been associated with the development of myocarditis and/or pericarditis, particularly in adolescents and young adults. Post-vaccination myocarditis is generally mild and is associated with a favourable clinical outcome in most cases.

The analysed data do not support any association between mRNA COVID-19 vaccines and sudden cardiac death in previously healthy young people.

No significant safety signals have been identified suggesting that acute myocardial infarction, venous thromboembolism, pulmonary embolism or stroke are potential adverse effects of COVID-19 vaccines.

All of the aforementioned conditions are known complications of COVID-19. Individuals who have had COVID-19 prior to vaccination or who remain unvaccinated are at increased risk of cardiovascular events during the two years following infection.

Many studies and hundreds of thousands of administered doses have demonstrated that mRNA COVID-19 vaccines are safe during pregnancy, both for the pregnant woman and the foetus.

Vaccination does not increase the risk of complications such as miscarriage or preterm birth.

In addition, it reduces the risk of hospitalisation and death in pregnant women and provides protection for their babies.

Side effects in pregnant women are similar to those observed in other vaccinated individuals. They are mostly mild to moderate and resolve within a few days.

Lactating women can be vaccinated without interrupting breastfeeding. An additional benefit is that the antibodies generated may be transferred to the foetus during pregnancy or to the newborn through breast milk.

Data indicate that COVID-19 vaccination may cause temporary changes in the menstrual cycle.

Studies have observed increases in cycle length of around 1-2 days following vaccination; however, these changes generally resolve within one or two subsequent cycles.

Some individuals have reported heavier menstrual bleeding after vaccination. However, these changes are typically short-lived and return to normal in subsequent cycles.

It is important to note that there is no evidence linking COVID-19 vaccines to long-term reproductive health problems or fertility issues.

In summary, although temporary, mild menstrual changes may occur after vaccination, they are not associated with long-term health problems.

Individuals who experience persistent or severe menstrual changes should consult a healthcare professional.

Current guidelines recommend waiting at least 3 months from the date of recovery before being vaccinated again.