Covid 19 coronavirus: Moderna announces vaccine breakthrough as more reinfections discovered

Moderna's experimental coronavirus vaccine appears to be safe and effective, company officials have revealed, but the news has come amid concerns about two more cases of reinfection.

The US company, whose vaccine uses messenger ribonucleic acid (mRNA) to make a protein that helps the immune system make antibodies against coronavirus, announced on Wednesday that its vaccine generates an immune response in all age groups.

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The vaccine, called mRNA-1273, is in Phase III of clinical trials, which is the last stage before regulatory approval.

The first phase of a trial to test the safety of the vaccine found only mild adverse effects and that it generated an immune response in volunteers aged 18 to 71, a Moderna officer told a meeting of the US Advisory Committee on Immunisation Practices, CNN reported.

Nurse Kathe Olmstead, right, gives volunteer Melissa Harting, of Harpersville, New York, an injection in the world's biggest study of a possible Covid-19 vaccine. AP Photo / Hans Pennink

The findings are especially significant for older people as they often have weaker responses to vaccines.

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The trial found the most common adverse reactions were fatigue, chills, headache and myalgia (muscle aches). There were some reports of adverse symptoms experienced after a second dose but the majority of these resolved within two days.

It comes after Prime Minister Scott Morrison walked back his comments that a vaccine would be "as mandatory as you can possibly make it" in Australia after signing a letter of intent with a separate potential vaccine being developed by AstraZeneca.

However, there are also concerns about the effectiveness of any potential vaccine after another two cases of reinfection were discovered.

The cases, in Belgium and the Netherlands, come a day after researchers in Hong Kong found a man was reinfected with a different strain of the virus months after he recovered from his first infection.

According to Reuters, the Belgian case involved a woman who contracted coronavirus in March and then again in June.

Virologist Professor Marc Van Ranst told the news agency that the woman in her 50s had very few antibodies after the first infection, although they might have limited the sickness.

The second case of reinfection was recorded in the Netherlands.

The National Institute for Public Health in the Netherlands announced the case – and virologist Marion Koopmans told Dutch broadcaster NOS the patient was an older person with a weakened immune system.

The cases have dampened expectations over how effective a vaccine will be over the long-term and have highlighted the possibility that people will need to get regular injections, similar to the annual flu jab.

"Covid-19 patients should not assume after they recover that they won't get infected again," microbiologist Kelvin Kai-Wang To, lead author of the Hong Kong study, told AFP.

Van Ranst said cases of reinfection were likely to be limited, although it was too early to tell.

While Covid-19 appears more stable than influenza it may still need more regular vaccinations.

"Viruses mutate and that means that a potential vaccine is not going to be a vaccine that will last forever, for 10 years, probably not even five years. Just as for flu, this will have to be redesigned quite regularly," Van Ranst said.

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Associate Professor of Microbiology Dr Taghrid Istivan at Melbourne's RMIT University said the reinfection of people highlighted the importance of vaccination and that multiple doses may be needed.

She also noted that the Hong Kong man did not have symptoms during the second infection, although antibodies were detected. During his first infection he did have symptoms but antibodies were not detected after his recovery.

"This may make us think if this is a reason behind the mystery cases that are driving community infections in Victoria, for example, as recovered individuals may get infected for a second time and spread the virus without noticing any symptoms," Istivan said.

"Therefore, PCR testing of asymptomatic individuals in hotspot areas and probably screening for immune responses in recovered patients may contribute to further knowledge on this."

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