A couple of months have now passed since the booster vaccine was administered. What is happening with immunity? Did the booster work? – Rita Vella

Studies have clearly shown that immunity against SARS-CoV2 tends to wane after three months from receiving a primary course of vaccination. This is especially so with the Omicron variant, which is now predominant all over the world.

Reports from the US, Israel and European centres show that, during both Delta- and Omicron-predominant periods, the third vaccine dose was highly effective at preventing COVID-19-associated emergency department and urgent care GP encounters. The average figures were 94 per cent for the Delta variant and 82 per cent for the Omicron variant. When it comes to hospitalisations, the booster dose prevented these in 94 per cent of cases for the Delta variant and 90 per cent for the Omicron variant. 

We have experienced this in Malta as well, where, despite the rise in cases of COVID-19 infection, the hospitalisation rates have remained well below the rates we saw during the pre-vaccination period. The emergence of the Omicron variant at around the same time that booster doses were recommended clearly shows the difference in vaccine effectiveness of the booster in countries where booster vaccination rates were high (such as Malta) and others where it was low.

Hospital admissions rose significantly in countries with a low booster uptake. With the increase in cases in the community, as expected, a number of persons requiring hospital admission for any other medical condition may test positive on admission. It is to be noted that less than 40 per cent of the positive patients at hospital are displaying COVID symptoms.

These findings highlight the importance of receiving a third dose of mRNA COVID-19 vaccine to prevent both moderately severe and severe COVID-19, especially while the Omicron variant is the predominant circulating variant. We now know that the effectiveness of two doses of mRNA vaccines and, especially two doses of other types of vaccine, is significantly reduced against this variant.

All unvaccinated persons should get vaccinated as soon as possible. All adults who have received their primary COVID-19 vaccination series and did not take the third dose (booster) should receive a third dose when eligible and eligible persons should stay up to date with COVID-19 vaccinations.

Why is Malta offering the fourth dose to some groups of people? – Marco Mizzi

There are groups of persons whose immune response provided by vaccination is not strong enough. This applies to all types of vaccinations. These include the severely immunocompromised and the very elderly. Severely immunocompromised persons are those who have received organ transplants, those with blood or solid organ cancers, those receiving treatment for rheumatological and severe inflammatory conditions and other immunosuppressive states due the medical condition or due to treatment.

In the very elderly, the immune system does not respond as well as in the younger population and the effectiveness of vaccination diminishes.

The risk of transmission in homes for the elderly is higher and, hence, the fourth dose is being offered to all elderly residents in homes for the elderly.

I had renal transplantation and am still receiving treatment. When should I take the fourth dose of the COVID-19 vaccine? – Jenny Sant

The latest international scientific recommendations are that people aged 12 and older who are moderately or severely immunocompromised should receive a total of four doses of mRNA COVID-19 vaccine. The fourth dose should be given at least three months after the third dose.

Will the fourth dose be offered to all the population? – Angela Xuereb

Studies analysing the benefits of a fourth dose in the general healthy population have not shown any significant benefits of this dose over and above the benefits of the third (booster) dose at this stage.

This has led the major vaccine manufacturers to start developing a vaccine which will specifically cover the Omicron variants as well as the earlier variants that were in circulation in 2021. In this way, the vaccine will target several variants at once.

Some companies, such as Pfizer and Moderna, have already declared that the development of such a vaccine is at a very advanced stage and is undergoing trials.